Power supplies, or ballasts, are known for gas discharge lamps. The known power supplies which provide a constant current for powering a gas discharge lamp are large, include many components, and are expensive. The present invention overcomes the disadvantages associated with the prior art by providing a compact, relatively inexpensive power supply for a gas discharge lamp which minimizes the components associated with the circuitry while providing both a high voltage starting circuit and a lower voltage running circuit for the gas discharge lamp.